1. Field of the Invention
This invention relates to a cycle crankset.
2. Description of the Related Art
Conventional cycle cranksets comprise two cranks that extend parallel to one another in opposite directions on both sides of a crankset shaft to which they are connected to drive in rotation during pedaling. At their free end, the cranks generally comprise securing means in the form of a threaded hole designed to accommodate the threaded end of a respective pedal shaft.
Just like the size of the frame, the length of the cranks corresponds to the morphology of the cyclist, in particular the length of the cyclist's legs. This crank length, however, cannot be directly proportional to leg length because technical parameters, such as, for example, ground clearance in turning, limit the possible variation.
Thus, the crank length generally varies in a total range of 170 to 180 mm, whereby the more common lengths are 170, 172.5 and 175 mm.
The length of the cranks is consequently generally fixed, which requires that the cyclist know—before purchasing the cycle—the recommended length for his use, on the one hand based on the length of his legs, and on the other hand based on the type of event in which he intends to participate. Actually, for example, a speed event over a short distance requires maximum power from the cyclist for a limited period, and this prompts him to increase the length of the lever arm defined by the cranks of the crankset and which corresponds to the distance or the distance between centers between the crankset shaft and the pedal shaft.
There is thus a need to be able to modify this distance between centers between the crankset shaft and the pedal shaft, and several devices are known that allow such a modification.
Thus, a certain number of devices are known in which an insert placed in a housing provided in the crank and comprising the threaded hole that accommodates the threaded end of the corresponding pedal shaft is used. The insert can be secured in different positions so as to make the distance between centers between the crankset shaft and the pedal shaft vary. This type of device is known from documents FR2416829, FR720835, WO99/67125, FR318003 and FR720834.
Another known device aims at optimizing the production of cranks by creating, starting from a fairly long common outline, different implantation positions for the threaded housing into which the threaded end of the pedal shaft is screwed to be secured there.
In the case of ultralight cranks made of composite materials, for example, it is also known to use an elongated metal insert to fill this role. Other more sophisticated devices exhibit a possible variation of the position of the pedal shaft by means of an eccentric or a spring barrel. Most of these additional devices involve only the single crank at the level of its connection, i.e., with the shaft of the crankset housing, or with the pedal shaft. The crankset shaft and the pedal shaft therefore remain unchanged in this case.
Also, another device of this type is known from FR 2 513 208, which describes a crankset in which a first and a second connection are secured in a bore that passes through each crank, starting from its two sides, with first and second assembly bores that are eccentric relative to the through bore. At least one of the assembly bores is provided with a threaded part that can be screwed into the shaft of the pedal, and an anti-rotation mechanism is provided to prevent the rotation of the connection. The connections are maintained on the crank with screws and optionally with a cup, said cup also being eccentric and placed opposite the threaded portion of the pedal shaft.
This device is also very bulky because it requires an element with threading that is designed to accommodate the pedal shaft, an element designed for the modification of the distance between centers, and additional securing elements, the entire unit in a limited space in the crosswise direction of the cycle, which is due to a maximum size for the spacing of the feet of the cyclist and therefore pedals.
All of these known devices comprise a very large number of parts machined with high precision, and, because of the masses of this additional device and the sizing of certain elements that should be sized to absorb very heavy stresses, among others the screwing torque of the pedal, the weight of the crank increases greatly.